15% minimum tip on the before-tax amount. 20% quite often. For restaurants. at a bar where I walk up and order a drink it's always without calculation for me. It often just depends on what kind of money I have on me if I'm paying cash. It's a good idea to separate kitchen performance from wait staff performance. There have been situations where the waiting experience was totally and completely to blame for a terrible experience and I've left 0. It's only ever happened once or twice in my life.

I don't believe that cash tips should be included in reported income and don't expect that any server should declare such earnings. It *is* supposed to be included. But then you're also supposed to declare all purchases, even of used items, at the end of the year to pay sales tax on them.

Store clerks get paid more than waiters pretty much... Everywhere. Some also make commission, as do many other sales jobs. That's their incentive.

When I worked at a restaurant, the kitchen staff all made a higher base wage than the wait staff.

People do also tip self-proprietors like photographers. That's not something I really do though unless they've brought along some underlings, in which case I may tip those employees.

There's a big difference between a tip and a bribe, but I don't like situations where the lines start to blur, which is the case in many places like Cuba. Nor do I like situations where someone throws themselves into the mix in order to squeeze a "tip" from you when in fact it's thinly disguised extortion. Example: parking your car downtown Lisbon and some guy will jump out as you're approaching a spot and point at it as if helping you park, afterwards expecting, and sometimes demanding some kind of compensation.

But as Doug mentioned I try to be respectful of local customs so as not to insult anyone, even if that means tipping lower than I normally would otherwise or perhaps not tipping at all if that's going to make them happier. Though I haven't yet met anyone that wasn't made happier with just a tiny bit of extra compensation.